This is something that always flummoxes me. I know how long a 42cm chain is (more or less), but if I am in a shop I have to try them on to see how they fall. When buying online, I tend to measure the ones I have at home to get more of an idea.
Looking at the diagram above, I tend to wear matinée and rope length. Because I have a big bust, the shorter ones either look tiny in the vast expanse, or dangle just on the precipice. The mid-chest and almost waist-lengths suit me way better.
How about you?